Electron-beam furnace with magnetic guidance and flux concentrator



March 12, 1963 c. w. HANKs 3,080,626

ELECTRON-BEAM FURNACE WITH MAGNETIC GUIDANCE AND FLUX CONCENTRATOR Filed May 27. 1960 3 Sheets-Sheet 2 C. W. HANKS ELECTRON-BEAM FURNACE WITH MAGNETIC GUIDANCE March 12, 1963 AND FLUX CONCENTRATOR 5 Sheets-Sheet 5 Filed May 2'?. 1960 INVENTOR. kf/vai.; (d 4m/z5 United tts 3,08il,626 ELECTRGN-BEAM FURNACE WITH MAGNETIQ GUIDANCE AND FLUX CONCENTRATR Charles W. Hanks, Orinda, Calif., assigner to Stauter Chemical Company, New York, NX., a corporation of Delaware Filed May 27, 196i), Ser. No. 32,328 6 Claims. (Cl. 22--57.2)

This invention relates to electron-beam furnaces Ifor heating materials by electron bombardment in a high vacuum, and particularly for melting materials :and casting ingots therefrom, with resulting purification, degasication to an exceptionally high degree, and other benets.

Briefly stated, electron-beam melting-and-casting furnaces include, within a continuously evacuated tank, a container for the molten material, which most commonly has the form of an annular, water-cooled casting mold open at its top and bottom ends. Solidilied material may `be progressively withdrawn `through the bottom end of the mold to bombard the material therein and maintain a molten pool of material atop the solidifying ingot. Preferably, melt stock is progressively fed into the beam above the open top end of the mold so that the melt stock is continually melted off as it advances into the electron beam. The so-melted material falls into the open top of the mold for continually replenishing the molten material in the pool.

The copending applications of Hugh R. Smith, I r. Serial No. 32,215, filed May 27, 1960, entitled Electron-Beam Furnace With Magnetically Guided Beam, and Charles W. Hanks, Serial No. 32,217, filed May 27, 1960, entitled Electron-Beam Furnace With Double-Coil Magnetic Beam Guidance, and Howard W. Howe, Serial No. 32,- 2,16, filed May 27, 1960, entitled Electron-Beam Furnace With Opposed-Field Magnetic Beam Guidance, all assigned to the same assignee as the present application,

` disclose and claim improved electron-beam furnaces comprising one or more electromagnet windings that provide a converging magnetic field for guiding electrons into the open top end of the mold.

The present invention yis a further improvement providing, yamong other advantages, a stronger magnetic eld in the immediate vicinity of the electron gun, so that the magnetic guidance is more effective upon the initial portions of the electron trajectories. Thus, any tendency for the electrons to move nonparallel to the magnetic flux lines is more forceably arrested near the electron gun, which assures a better focus `of the beam and less spiralling of the electr-on paths within the magnetic field in the vicinity of the casting mold. Another object and advantage of this invention is that the shape of the magnetic field can lbe altered somewhat to facilitate variations in the size, shape, and placement of the electron gun, the placement of the melt stock, and the like. Still another object and advantage is the reduction in size of the electromagnet windings relative to the magnetic field strength desired, and the reduction of electric power needed to energize the windings.

In accordance with the present invention, a flux concent-rator of ferromagnetic material is arranged adjacent to the electron gun for increasing the magnetic field strength in the vicinity of the gun. A preferred form is a horizontal ring of ferromagnetic material disposed just above an annular electron gun, in vertical, coaxial alignment therewith Vand with the casting mold, connected through a ferromagnetic yoke to another ring of ferromagnetic material coaxially surrounding the casting mold below the electromagnet windings.

The foregoing and other aspects of the invention will 3,080,626 Patented Mar. 12, 1963 be understood better from the following illustrative description and the accompanying drawings.

FIG. l of the drawings is a highly schematic, vertical section of an improved electron-beam furnace.

FIG. 2 is a fragmentary schematic, vertical section of the same furnace, drawn to a somewhat larger scale, Ishowing typical magnetic flux lines and electron trajectories.

FIG. 3 is a fragmentary schematic, vertical section of another improved electron-beam furnace.

Referring to FIGS. 1 and 2, an annular copper mold 1, with its axis vertical, has open upper and lower ends and is provided with a water jacket 2 through which water or other coolant is continually circulated by conventional means (not shown), whereby the mold is cooled to solidify molten material therein. Other parts of the furnace may also be water-cooled, as desired, such being accomplished by obvious means requiring no description. The solidified material may be progressively withdrawn through the open bottom end of mold 1 to form a cast ingot 3 of progressively increasing length, which may be cut off from time to time as desired. Progressive withdrawal of the ingot is accomplished, for example, by means of rollers 4 driven by `an electric motor 5.

A first annular electromagnet winding 6 extends coaxially around mold 1, as shown, and has a vertical axis concentric with the open top lof the mold. Preferably, this winding is protected by an inner sheath 7 of insulation and an outer sheath 8 of metal. Wires 9 and 10 connect winding 6 to a D.C. power supply- 11 in `series with a rheostat 12, whereby the winding 6 is supplied with energizing direct current of adjustable magnitude. A second electromagnet winding 13 is vertically spaced above the first winding, in vertical coaxial alignment with the lirst winding 6 and the `'annular' mold 1. Preferably, winding 13 is protected by an inner sheath 14 of insulation and yan outer sheath 15 of metal. Wires 16 and 17 connect winding 13 to D.C. power supp-ly 11 in series with a rheostat 18, whereby Winding 13 is supplied with energizing direct current of adjustable magnitude. The two windings 6 and 13 are energized in additive magnetic flux relation, and the energizing currents supplied to the two windings are individually adjustable by means of rheostats 12 and 18. The so-energized windings produce -a magnetic eld having magnetic flux lines that extend and converge downwardly through the center opening of winding 13 into the open top end of mold 1, as represented by the broken lines 19, FIG. 2.

An .annular electron gun, vertically spaced above winding 13 in vertical coaxial alignment therewith and with mold 1, directs la beam of electrons along the magnetic flux lines 19 that converge into the open top end of the casting mold. In its preferred form, the electron gun comprises an annular thermionic cathode 20, most commonly made from a horizontal loop of tungsten wire, connected through leads 21 and 22 and a transformer 23 to an `alternating-current supply 24, which provides alternating current through wire 20 for heating the same to thermionic-emission temperature. An accelerating electrode 25 is closely spaced ybelow cathode 20 and a focusing electrode 26 is closely spaced above cathode 2t), as shown. Preferably, all parts of the gun `are made of essentially nonrnagnetic materials.

Electrical connections are provided for maintaining accelerating electrode 25 at substantially the same elect-ric potential las mold 1, preferably ground potential. This is indicated schematically in the drawing by ground connection symbols 27 and 28. Cathode 2G and focusing electrode 26 are maintained at substantial negative potentials, commonly 5,000 to 15,00() volts, relative to the accelerating electrode. This is accomplished, for example, byY

The overall design of the electron gun may be similar Y to that described in the copending patent application of Charles W. Hanks, Serial No. 818,306', filed June 5, 1959, and assigned to the same assignee :as the present application. .In the present furnace employing a magnetic eld t'o guide the electron beam, the cathode, accelerating electrode, and focusing electrode are shaped and aligned to direct electrons downwardly and inwardly parallel `to the converging magnetic lines of force 1 9, forming' a hollow, conelike electron beam, and thereafter the magnetic field plays KAa significant part in focusing and guiding the electron beam into the open -topjend of mold 1. s

4 A horizontal feed trough 32 extends inwardly above mold 1 between the vertically spaced windings 6 and 13.

' Discharge end 32 is adjacent to the open top end of the mold. This feed trough A(and thereby its contents) is electrically grounded as indicated by the conventional symbol at 33. Melt stock 34 in any convenient form, eg., rods, bars, blocks of compacted powdenetc., is Ifed through trough 32 into one side of the electron beam entering Imold v1. -Feedmechanism is symbolized by rollers 35 driven by an electric motor 36. As the melt stock emerges from the discharge end of the feed trough, it is bombarded andY melted away by the electron beam.k The.

sofmelted materialy falls into the open end of mold 1 for continually replenishing a pool 3' of molten material which rests on top 'of cast ingot 3 and is supported within Y the casting mold 1 below electromagnet winding V6, and

ring 38 is disposed immediately above the annular electron gun and in vertical coaxial alignment therewith. Yoke 3 9 passesvoutside of annular windings 6 and 13. Parts 2,6 and 33 `are spaced .apart sufficiently foielectrical insulation lpurposes.

, The ilux 'concentraton and ringl38 in particular,V is

shaped and aligned to lower the reluctance of magneticy flux paths passing through the electron gun relative to other ilux paths,- thereby increasing the magnetic field strength in thefrvicinity of the electron gun. This 'signicantly increases the effectiveness of the magnetic field guidance upon the initial portions of thel electronY pathsnear the gunand imposes a more forcefulrestraint Iupon 'any substantial departure of the electron paths `from parallelism with the magnetic flux lines. The additional magnetic restraint :and` guidanceupon the initial portions of the electron paths provides a substantial improvement iny beam focus in the vicinity of the casting mold and, in particular, reducesspiralling ofi'the electron paths within the'magneticiield. Itv will berunderstood of course, that this improvement is not limited in its application to furnaces employing the yparticular type of double-coil guidance illustrated in FIGS. l :and 2, but may also be ap.- plied, for example, to furnaces in which the upper winding isornitted, as shown in applioation Serial No. 32,215,

Yand tofu'rnaces wherein the two coilsjare energized in bearn'isv represented by the shading between linesAtl andV Hand between lines 4Z and 43.1.It willbe noted that the beam is everywhere,substantially'parallel to the magnetic Viiux lines V19 thatconvergev and exteridjthrough the center opening-"of-.winding 13 intothe open top end ofV mold 1.

In FIG. 1, there is `schematically shown a vacuum tank 44 which encloses the casting mold 1, the electron gun, and associated parts. Tank 44 is continuously evacuated to a high vacuum, preferably one micron of mercury absolute pressure or less, by connection through a largearea duct 45 to high-capacity vacuum pumps 46. vAppropriate air locks (not shown) may be provided as desired for the introduction of melt stock, the removal'of ingots, the replacement of electron guns, and the like.

FIG. 3 shows a modification wherein the iiux concentrator serves the additional purpose of atlering the shape of the magnetic iield so that the converging ux lines that guide the electron beam extend downwardly and inwardly toward the open top end of theV casting mold at smaller angles to the horizontal. This is especially advantageous when the melt stock is to be introduced as a vertical rod extending downward in coaxial alignment with the casting mold. The casting mold 1, cast ingot 3, and winding 6 may be identical to the corresponding parts shown in FIG. 2. An annular electron gun comprises cathode 47, 'accelerating electrode 48, and focusing electrode `49. The

Yelectron gun may be similiar to the annular gun shown in FIG. 2, except that in FIG. 3 the gun is spaced much closer to the casting mold relative to the diameter ofthe gun, ywhich may be somewhat larger in thisembodiment. Y The ux concentrator comprises two horizontal rings 50 and 51 of ferromagnetic material connectedtogether by a ferromagnetic yoke 52, which, it will be noted, passes outside of windingv 6. Ring 50 extends coaxially around mold 1 below winding 6 whereas ring 5.1 is disposedimmediately'above and outside ofthe annular electron gun (spaced therefrom j-ust enough forelectrical insulation) so as to concentrate the magnetic Iflux along pathspassing through the gun. Typical iiux paths are represented by broken lines 53, and the electron beam occupies the volume representedvby the shaded area between lines 54 and 55 and between lines 56 and 57,V ,It will benoted that the electron paths extend downwardly and inwardly at an angle of about 45 to the horizontal.

The melt stock is a vertical rod 58 fed downwardly through the annular gun Vintothe hollow conelike electron beam, in vertical coaxial alignment above thel open top of'mold 1.A As the lcwer end of Aro'd'58 advancesinto the beam, it is melted away and the so-melted material drops into the open top end of mold 1 for maintaining la pool 3 of molten material atop the, newly cast Vingot 3. Feed mechanism for the' melt stock is symbolized by the rollers 59 driven by electric motortl. The smelt ,stock may be carried out, and that Lfurther changesand modiiications are possible without `departing from the inve'n? tive principles herein disclosed.

What is claimed is: L

1. An'electron-beam furnace comprising a container Y for molten material, said container having anv open top, means providing la magnetic eld having flux` lines converging into said container through its opentop, an elect'ron .gun aligned to project a bearnof `electrons along said converging'flux lines into said container, ra tf-rst'ux con-Y 'oentrat'or' of ferromagneticrnaterial adjacentV to saidV gun,

a second flux concentrator of ferromagneticmaterial padjacent the container, ak yokerofYferromagneticfmaterial connecting the first and secondfluizrV concentratorsfor in,V creasing fthermagnetic lliel'd strength in the vicinity of the' gun'and between the twoy concentrators, YaY vacuum tank Vvenclosing at least thespacebetween said gun and said container, and means for eyacuating saidI tank continue l ously."

`2. An electron-beam furnace as in claim 1, said means supplying a magnetic iield comprising an electromagnet winding extending yaround said container and having a vertical axis substantially concentric with said open top, said rst iux concentrator comprising a ring of ferromagnetic material in vertical, coaxial alignment with said winding, said electron gun being annular and lying between said ring and said winding.

3. An electron-beam furnace comprising an annular container for molten material, said container having a vertical axis and an open top end, :a tirst ring of ferromagnetic material extending -around said container, a second ring of ferromagnetic material vertically spaced .above the open top end of said container, a yoke of ferromagnetic material connecting said rings, means providing between said rings a magnetic eld having tiux lines extending through the open top of said container, an electron gun disposed and aligned to project a beam of electrons along said ilux lines into said container, a vacuum tank enclosing at least the space between said gun and said container, and means for evacuating `said tank conltinuously.

4. An electron-beam furnace comprising an annular metal mold having a vertical axis and having `an open top end |for receiving melted material, an annular electromagnet winding extending coaxially around said mold below said open top end, a iirst horizontal ring of ferromagnetic material extending coaxially around said mold below said winding, `an annular electron gun vertically spaced above-the open top end of said mold in Vertical coaxial alignment lwith the mold land said winding, a second horizontal ring of ferromagnetic material closely spaced above said gun in vertical coaxial alignment therewith, a yoke of ferromagnetic material connecting said rst and -second rings and extending outside of said winding, directcurrent supply means connected to energize said winding, the so-energized winding providing between said rings a magnetic field having linx lines extending and converging downwardly through the open 4top end of said mold, said electron gun being shaped and aligned to direct a hollow, conelike beam of electrons downward and inward along said converging flux lines, means for progressively vfeeding material to be melted into the electron beam above the open top end of said mold, a vacuum tank enclosing `said electron `gun and said mold and the space therebetween, and means for continuously evacuating said tank.

5. An electron-beam furnace as in claim 4, additionally comprising a second electromagnet winding vertically spaced vabove the open top end of said mold and below said electron gun, the two windings being in vertical c0- iaxial alignment, land means energizing said second winding in additive magnetic flux relation to the first winding.

6. An electron-beam furnace as in claim 4, the inside diameter of said second ring being larger than the vertical spacing between said second ring and the top end of said mold, the melt stock being fed vertically downward through the center of said second ring and said :annular electron gun.

References Cited in the ile of this patent UNITED STATES PATENTS 2,321,886 Anderson June l5, 1943 2,423,729 Ruhle July 8, 1947 2,640,948 Burrill June 2, 41953 2,793,281 Steigerwald May 21, 1957 2,845,371 Smith July 29, 1958 2,897,396 Von Ardenne July 28, `'1959 2,880,483 Hanks et al. Apr. 7, 1959 OTHER REFERENCES American Machinist, reprint from issues of February 23, 1959, and March 9, 1959, pp. 2, 3 and 4. 

1. AN ELECTRON-BEAM FURNACE COMPRISING A CONTAINER FOR MOLTEN MATERIAL, SAID CONTAINER HAVING AN OPEN TOP, MEANS PROVIDING A MAGNETIC FIELD HAVING FLUX LINES CONVERGING INTO SAID CONTAINER THROUGH ITS OPEN TOP, AN ELECTRON GUN ALIGNED TO PROJECT A BEAM OF ELECTRONS ALONG SAID CONVERGING FLUX LINES INTO SAID CONTAINER, A FIRST FLUX CONCENTRATOR OF FERROMAGNETIC MATERIAL ADJACENT TO SAID GUN, A SECOND FLUX CONCENTRATOR OF FERROMAGNETIC MATERIAL ADJACENT THE CONTAINER, A YOKE OF FERROMAGNETIC MATERIAL CONNECTING THE FIRST AND SECOND FLUX CONCENTRATORS FOR INCREASING THE MAGNETIC FIELD STRENGTH IN THE VICINITY OF THE GUN AND BETWEEN THE TWO CONCENTRATORS, A VACUUM TANK ENCLOSING AT LEAST THE SPACE BETWEEN SAID GUN AND SAID CONTAINER, AND MEANS FOR EVACUATING SAID TANK CONTINUOUSLY. 